The subject matter of the present invention is a method of preparing trialkyl organo-oxysilanes of Formula I R.sub.3 SiOR' by the esterification of trialkyl halogen silanes of Formula II R.sub.3 SiHal with organic hydroxy compounds of formula III R'OH with the release of gaseous hydrogen chloride.
In the above formulas, R represents identical or different aliphatic alkyl moieties of 1 to 4 carbon atoms, which can be either saturated or unsaturated and/or branched. R' represents a saturated or unsaturated aliphatic alkyl or acyl moiety, which also can be branched and/or cyclic and/or can contain ether oxygen bridges or ester groups, or can be aromatically substituted, or R' can represent an aromatic aryl or aroyl moiety which can bear hydrocarbon and/or halogen substituents and/or nitro substituents.
It is known that trialkylchlorosilanes react poorly with organic hydroxy compounds (cf. J. Org. Chem. 23 (1958), 50 to 58). Especially the complete reaction encounters the difficulty that the trialkyl organo-oxysilane that develops reacts with the nascent halogen hydride to form the starting substances, so that a certain amount of trialkyl halogen silane and hydroxy educt always remains in the reaction mixture. To remedy this disadvantage it has been proposed that the esterification reaction of trialkyl chlorosilanes with alcohols be performed in the presence of acid acceptors in order to bring the reaction to completion (J. Chem. Soc. 1956, 1536 to 1539, or J. Org. Chem. 23 (1958), 50 to 58). These known methods however, have the disadvantage of the inevitable production of ammonium chlorides, which reduce the yield on account of their adsorptive properties; furthermore, the separation of the ammonium chlorides from the reaction mixture involves a great deal of difficulty.
The procedure described in German Federal OS No. 30 00 782, of limiting the above-described re-formation of trimethylchlorosilanes by use of an excess of alcohol, leads to secondary reactions whereby disiloxane and alkyl or acyl chloride are formed, and hence it leads to losses of yield. This latter method is usable for tetrachlorosilanes and trichlorosilanes and, under certain circumstances for dichlorosilanes within narrowly defined conditions, but it is not suited for the esterification of trialkyl chlorosilanes. This is because in this case large percentages of alkyl and acyl chlorides and disiloxanes are formed, while trialkylsilyl esters are obtained in only a low yield.
The problem therefore existed of finding a generally usable method for the esterification of trialkyl halogen silanes with organic hydroxy compounds, which will not have the disadvantages described above, and will give yields permitting economical technical utilization.